The present invention relates to an imaging lens for forming an image on an imaging element such as a CCD sensor and a CMOS sensor. In particular, the present invention relates to an imaging lens suitable for mounting in a relatively small camera such as a cellular phone, a digital still camera, a portable information terminal, a security camera, an onboard camera, and a network camera.
An imaging lens to be mounted in a small camera has been required to have a high-resolution lens configuration suitable for a recently developed imaging element with a higher resolution, as well as to have a smaller size. Conventionally, various lens configurations have been proposed. Among the various lens configurations, a configuration formed of three lenses has been suitable for miniaturization and easy to correct various aberrations properly, and has been applied to many cameras.
An imaging lens disclosed in Patent Reference has been known as an imaging lens having such a three-lens configuration. The imaging lens disclosed in Patent Reference includes a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power arranged in this order from an object side. In the configuration, the third lens has a shorter focal length relative to that of a whole lens system, that is, the third lens has relatively strong refractive power. Further, the first lens has refractive power stronger than that of the second lens. Accordingly, it is possible to correct a field curvature or coma aberration.    Patent Reference: Japanese Patent Application Publication No. 2008-76594
In recent years, miniaturization and resolution increase of cellular phones and cameras have been rapidly advanced, and even an imaging lens has been increasingly required to have more advanced performances than before. The imaging lens disclosed in Patent Reference has been known to properly correct aberration. However, the lens system has a relatively long focal length. Accordingly, it is difficult to reduce a distance of an optical axis from a surface of the first lens on the object side to an image plane. Therefore, it is difficult to achieve both miniaturization and satisfactory aberration correction.
In view of the problems of the conventional techniques described above, an object of the present invention is to provide an imaging lens with a small size capable of properly correcting aberration.